The research is currently concerned with utilizing the information on the ultrastructural morphology and properties of tooth enamel developed in previous years of this project to gain an understanding of enamel malformation, enamel crystal dissolution, and enamel repair. Our long-term hypothesis is that the enamel crystal's nucleation, growth, orientation, and arrangement (into prisms) is dependent on a unique relationship of the crystal to the organic matrix and the ameloblast. It is our aim to clarify the ultrastructural arrangement and disarrangement of these enamel tissue components in normal and pathological states in developing and mature enamel. TEM results will be directly correlated with other observations and techniques [e.g. clinical, contact microradiography (CMR), light microscopy (LM), and scanning electron microscopy (SEM)]. Our specific aims are (a) using the subameloblastic cyst induced in developing rat molar as a useful model to examine ultrastructural enamel histopathology, and (b) determining optimal treatments for enamel repair by clarifying the ultrastructure of enamel tissue especially during demineralization/remineralization. Subameloblastic Cysts in Developing Rat Molar - NaF - studies using sodium fluoride to induce cysts and defective enamel will be extended to follow recovery process, evaluate surface, determine density and crystal size at secretory and maturation stages. Diphosphonates - studies focused on cellular versus direct crystal effects during secretory and maturation stages. O2 levels - newborn rats will be in a reduced oxygen atmosphere to determine effects of rat enamel development both alone and in combination with NaF and diphosphonates. Mature Human Enamel - Demineralized, Remineralized, Defective: Diphosphonates - Surface Effects - experiments using 2 diphosphonates (EHDP, Cl2MDP) on mature enamel surfaces, before and after acid etching. SEM results will be supplemented with CMS and TEM. Demineralization/Remineralization/Caries - initial experiments with bovine enamel will be redirected to en bloc treatment of mature human enamel. Changes will be evaluated by CMR and TEM and compared with precarious and normal enamel. Enamel Tufts - ongoing acid (TCA) and EDTA (pH 7.2) experiments will be modified to determine distribution of remaining crystals. Histopathology - deciduous teeth and permanent teeth with enamel defects will be examined and compared to controls and to rat molar experiments.